1. Field of the Invention
The invention relates to apparatus and methods for facilitating total hip arthroplasty.
2. Background Information
Hip arthritis due to malfunctions, fractures and diseases constitute a major source of disability. Reconstruction of the hip, whether involving first time hip replacement or replacement of failed components, is complicated by the great mobility of the hip joint and the uncertainty in the exact position of pelvis and femur during surgery. When a hip joint is replaced, as in total hip arthroplasty, critical factors to assess include changes in leg length, tension of the tissues around the joint, and stability of the replaced hip or its resistance to disassembly, referred to as hip dislocation. These critical factors are generally checked by means of a “trial reduction” (i.e., an insertion of the prosthetic femoral head into the prosthetic acetabulum). It is during this trial reduction that these critical parameters can be assessed to determine if the goals of the reconstruction are being achieved.
This assessment includes moving the femur with respect to the pelvis over ranges of motions, including flexion/extension, adduction/abduction and internal/external rotation. The trial reduction can be used to generally assess leg length, tissue tension, and limits of motion. For example, motion may be limited by tethering of tissues coming under tension, impingement of the prostheses against each other (prosthetic impingement), impingement of the tissues themselves (nonprosthetic impingement), or dislocation of the prosthetic femoral head out of the prosthetic acetabular socket in the absence of, or in advance of, prosthetic impingement.
On detection of unacceptable changes in length, or of an unsafe or restricted range of motion, corrections must be made and the process repeated. This prolongs the operation. Further, failure to optimally place the implants within the body can result in instability of the prosthetic joint or in inappropriate leg length, both of which may require reoperation.